Is a low heart rate worrisome?

Ask the doctor

Q. I've read that a normal resting heart rate is between 60 and 100 beats per minute. Mine runs around 45 to 48. Should I be concerned? I have been a runner for 42 years and have completed seven marathons.

A. Unless you feel tired, dizzy, or weak, there's usually no cause for concern, especially because it sounds like you're in good physical shape.

Endurance athletes and other people who exercise a great deal often have lower-than-average heart rates, sometimes even below 40 beats per minute. Exercise strengthens the heart muscle, enabling it to pump a greater volume of blood with each heartbeat. More oxygen gets delivered to the muscles, so the heart needs to beat fewer times than it would in a less-fit person while at rest.

In general, a slower resting heart rate (or low pulse rate) is better than a fast one. A high resting heart rate has been linked to atherosclerosis, sudden death, and an increased risk of dying from cardiovascular disease. In people who are not physically active, a resting heart rate below 60 is sometimes a sign of an electrical problem with the heart, a low thyroid level (hypothyroidism), or damage from a heart attack or heart disease.

- Deepak L. Bhatt, MD, MPH
Editor in chief
Harvard Heart Letter